Well, even in windows, if totally freeze, ctl+alt+del can't help it. So same thing in Linux, if totally freeze, you can't do anything either. But if only the X-server freeze, press ctl+alt+backspace to kill the X-server. If nothing happen, then it's more likely that your redhat freeze totally and u can't do anything.
Try to update all the patches they gave, including the kernel and it'll seem to become more stable.
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